It's understandable. When you commit your life to something—anything—it's hard to let go.
When athletes retire, some of them experience a loss of purpose, a loss of identity. They don't know what they're supposed to do next because they've dedicated their lives to the sole purpose of achieving athletic immortality. And when their time is up, they find themselves unable to say goodbye—so to make life easier, they just come back.
Unfortunately, those decisions to un-retire tend to backfire.
Such is the case with these 20 athletes.